Project Summary The search for a cure for HIV remains a priority within the scientific community. Key to a cure is an understanding of the mechanisms underlying the development of latent reservoirs. My ongoing K01 SERCA work has focused on defining the effect of activated platelets on the development of latent viral reservoirs, with an emphasis on the sanctuary organ of the brain, through work with in vitro systems and SIV-infected macaque models. My K01 SERCA data demonstrate that direct interactions with platelets affect monocytes and endothelium differently, and selective inhibition of platelet-monocyte aggreagates (PMAs) while preserving the presence of platelet-endothelial associations (PEAs) may be key to effectively controlling the development and reseeding of latent viral reservoirs. However, parsing apart the mechanisms that mediate these interactions has proven challenging with the tools currently in my arsenal. To do so, I require an animal model in which 1) all components of the animal are of a common species origin, allowing for physiologically relevant interactions between platelets, monocytes, endothelium and other aspects of the immune system, 2) genetic modifications are feasible, thus allowing for the definition of mechanism through work with animals lacking components of the pathway of interest, and 3) the animal can be maintained under a variety of conditions, allowing for the study of environmental influences, such as microbiome, on the mechanisms of interest. The overarching goal of this R03 proposal is thus to work with the EcoHIV-infected mouse model in my lab to complement and build upon my ongoing K01-funded macaque and in vitro work. EcoHIV is a chimeric virus in which HIV-1 gp120 has been replaced with ecotropic murine leukemia virus gp80, conferring specific tropism for mouse cells. EcoHIV infection in immunocompetent mice mirrors many aspects of HIV pathogenesis, including, as I demonstrate in my preliminary data, the formation of PMAs. In my first aim, I propose to work with the EcoHIV-infected mouse to define how platelets interact with monocytes and endothelial cells in the context of HIV, and to determine how these interactions can be inhibited. This aim will inform a future R01 application to propose targeted therapeutic interventions to interrup PMAs while preserving PEAs to prevent the establishment of a latent reservoir in the brain. In my second aim, I hypothesize that platelet activation in HIV infected individuals may be driven by elements of the gastrointestinal microbiome, and t ultimately the formation of PMAs and/or PEAs. I will model platelet activation in HIV infection under defined microbial conditions with EcoHIV infected, immune competent, germ-free mice so that this hypothesis can be tested. This aim will result in a second R01 application to define the elements of the microbiome that drive platelet activation in the context of HIV infection. Thus this R03 proposal will serve as a critical final step towards independence in my career as a veterinarian- scientist, simultaneously building on my K01 SERCA work and expanding my research into novel directions.